One known method for determining relative humidity consists in looking up a psychrometric chart knowing the dry bulb temperature and wet bulb temperature. To measure wet bulb temperature, a thermometer (e.g., thermocouple) has its bulb wrapped in a cloth (i.e., sock) that is kept wet with water via wicking action. Such an instrument is called a wet bulb thermometer.
In practice, numerous conditions must be met in order to ensure the precision of the reading obtained with the wet bulb thermometer, notably to protect the sock from dust, and ensuring that the sock is always humid. For instance, the wet bulb temperature reading must be taken when the water on the sock is at the wet bulb temperature of the air. Therefore, systems have been developed for industrial applications to continously feed water to the sock. However, the feed of water may saturate the sock with water, not allowing the water of the sock to warm up to the wet-bulb temperature of the air. Moreover, in industrial applications such as in driers, ovens, or the like, in which there may be a non-negligible amount of air-borne dust particles resulting from a process, the readings obtained from the wet bulb thermometer may be affected if a crust of dust particles forms on the sock.